Scenarios limiting global warming to 1.5°C describe major transformations in energy supply and everrising energy demand. Here we provide a contrasting perspective by developing a narrative of future change based on observable trends that results in low energy demand. We describe and quantify changes in activity levels and energy intensity in the Global North and South for all major energy services. We project that global final energy demand by 2050 reduces to 245 EJ, around 40% lower than today despite rising population, income and activity. Using an integrated assessment modelling framework, we show how changes in the quantity and type of energy services drive structural change in intermediate and upstream supply sectors (energy and land use). Down-sizing the global energy system dramatically improves the feasibility of low-carbon supply-side transformation. Our scenario meets the 1.5°C climate target as well as many Sustainable Development Goals, without relying on negative emission technologies. * Contingency reserve of 8 EJ is allocated equally to Global North and South respectively. Bunker fuels are reported at the global level only, consistent with current energy balances and emission accounting frameworks. Activity level units vary per end-use service and upstream sector: a billion m 2 of floor space; b trillion passengerkilometres; c billion tonnes of materials; d trillion tonne-kilometres.

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Low-carbon investments are necessary for driving the energy system transformation called for by both the Paris Agreement and Sustainable Development Goals. Improving understanding of the scale and nature of these investments under diverging technology and policy futures is therefore of great importance to decision makers. Here, using six global modelling frameworks, we show that the pronounced reallocation of the investment portfolio required to transform the energy system will not be initiated by the current suite of countries' Nationally Determined Contributions. Charting a course toward 'well below 2 °C' instead sees low-carbon investments overtaking fossil investments globally by around 2025 or before and growing significantly thereafter. Pursuing the 1.5 °C target demands a marked up-scaling in low-carbon capital beyond that of a 2 °C-consistent future. Actions consistent with an energy transformation would increase the costs of achieving energy access and food security goals but reduce those for achieving air quality goals.

<p><strong>Abstract.</strong> This paper presents the first comprehensive assessment of historical (1990–2010) global anthropogenic particulate matter (PM) emissions including consistent and harmonized calculation of mass-based size distribution (PM<sub>1</sub>, PM<sub>2.5</sub>, PM<sub>10</sub>) as well as primary carbonaceous aerosols including black carbon (BC) and organic carbon (OC). The estimates were developed with the integrated assessment model GAINS, where source- and region-specific technology characteristics are explicitly included. This assessment includes a number of previously unaccounted or often misallocated emission sources, i.e., kerosene lamps, gas flaring, diesel generators, trash burning; some of them were reported in the past for selected regions or in the context of a particular pollutant or sector but not included as part of a total estimate. Spatially, emissions were calculated for 170 source regions (as well as international shipping), presented for 25 global regions, and allocated to 0.5° x 0.5° longitude-latitude grids. No independent estimates of emissions from forest fires and savannah burning are provided and neither windblown dust nor unpaved roads emissions are included. <br><br> We estimate that global emissions of PM have not changed significantly between 1990 and 2010, showing a strong decoupling from the global increase in energy consumption and consequently, CO<sub>2</sub> emissions but there are significantly different regional trends, with a particularly strong increase in East Asia and Africa and a strong decline in Europe, North America and Pacific. This in turn resulted in important changes in the spatial pattern of PM burden, e.g., European, North American, and Pacific contributions to global emissions dropped from nearly 30 % in 1990 to well below 15 % in 2010, while Asia's contribution grew from just over 50 % to nearly 2/3 of the global total in 2010. For all considered PM species, Asian sources represented over 60 % of the global anthropogenic total, and residential combustion was the most important sector contributing about 60 % for BC and OC, 45 % for PM<sub>2.5</sub> and less than 40 % for PM<sub>10</sub> where large combustion sources and industrial processes are equally important. Global anthropogenic emissions of BC were estimated at about 6.6 and 7.2 Tg in 2000 and 2010, respectively, and represent about 15 % of PM<sub>2.5</sub> but for some sources reach nearly 50 %, i.e., transport sector. Our global BC numbers are higher than previously published owing primarily to inclusion of new sources. <br><br> This PM estimate fills the gap in emission data and emission source characterization required in air quality and climate modelling studies and health impact assessments at a regional and global level, as it includes both carbonaceous and non-carbonaceous constituents of primary particulate matter emissions. The developed emission data set has been used in several regional and global atmospheric transport and climate model simulations within the ECLIPSE (Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants) project and beyond, serves better parameterization of the global integrated assessment models with respect to representation of black carbon and organic carbon emissions, and built a basis for recently published global particulate number estimates.</p>

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